This invention generally concernes transmission systems of motor vehicles and more particularly to clutch control circuits for automatic engagement and disengagement of clutches in the transmissions to permit gear change operation of the transmissions.
A variety of clutch control systems are proposed for automatic control or actuation of clutches which do not require attention of the driver and simplify gear shift operation by him. A typical arrangement of them is that a clutch forming part of the clutch control circuit is mounted on the gear shift lever so that the clutch is engaged and disengaged in direct response to manipulation of the gear shift lever by the driver. As soon as the gear shift lever is touched or grasped by the manipulator, an automatic clutch is disengaged enabling manual or power-assisted gear shift operation. When the driver takes his hand off the gear shift lever after completing the gear shift operation, the clutch is again engaged for transmitting torque of engine to the transmission. Other switches indicative of engine operating condition such as engine acceleration may additionally be provided, if desired.
In such arrangement, there is a difficulty in that some failure or breakage at any one switch or at any part of the circuit line immediately disables the engagement and disengagement of the clutch being required for gear shift operations. This results in that shift operation is rendered difficult, particularly from the neutral position to any drive position.